PostGIS

PostGIS has been developed by Refractions Research as a project in open source spatial database technology. PostGIS is released under the GNU General Public License. PostGIS adds support for geographic objects to the PostgreSQL object-relational database. In effect, PostGIS "spatially enables" the PostgreSQL server, allowing it to be used as a backend spatial database for geographic information systems (GIS), much like ESRI's SDE or Oracle's Spatial extension.